Method and apparatus for implementing TDM fuzzy control

ABSTRACT

Apparatus requiring a plurality of control signals is provided with a fuzzy logic controller. The fuzzy logic controller is programmed with a plurality of control functions. Respective parameters determinative of the control signals are applied to the fuzzy controller in time division multiplex fashion, and concurrently respective control signals provided by the fuzzy controller are time division multiplex applied to respective control signal paths.

The present invention relates to a control method and to a controlcircuit which effects control using fuzzy logic.

BACKGROUND OF THE INVENTION

An article by Gunter Trautzl having the title "Unscharfe Logic: FuzzyLogic" has appeared in "der electroniker", No. 3, 1990 at pages 39-43.

In addition to the expression Fuzzy logic for the term "unscharfeLogic", the names, Rule-Base-System, ambivalent logic and multiple valuelogic are common.

Fuzzy logic had been developed by 1965 in order to be able to alsoprocess sets of data that were incomplete or inexact. To this end, withthe help of a functional relationship which is often referred to as aMembership-function, the control signal for a control circuit isobtained, for example, from a table of values.

In the said document, this control method is explained on the basis of acarriage on which a bar carrying a mass is fixed so as to be pivotal inthe direction of movement of the carriage. The carriage is moved in ahorizontal direction by the control circuit such that the bar carryingthe mass does not fall over but rather is counter-balanced. Expressed inother words, this means that the carriage imitates the balancing abilityof an acrobat who tries to balance a bar in the hollow of his hand.

The status of the bar is described by its angular speed and its angle ofdeflection which represent the input variables for the controller. Theoutput variable is the speed of the carriage.

This control circuit is described in the following words in the saiddocument:

"The set-up by means of fuzzy logic is as follows: The system has thetwo input variables, angle θ and angular speed w and an output variable,speed v. To start with, one gathers together all the input and outputvariables according to their values into groups and also provides thefunctional relationship thereof. For example, one splits the angle intothe values, large-positive, middle-positive, small-positive, zero,small-negative, middle-negative, large-negative. Therein, by large, wemean all angles from 20 to 90 degrees (theoretical limit), by middle,all angles between 5 and 25 degrees, by small, all angles between 0 and10 degrees, as zero, one admits all values between -0.5 degrees and +0.5degrees. The Membership-function for large is such that, for example,all values above 45 degrees have the relationship factor of 1, but therelationship then drops in order to lie at 0.005 at 20 degrees. Therange of values for w and for v is defined in a similar manner. In thisway, one achieves an association of the system variables with theMembership-function.

The second part of the set-up for the solution consists in that a systemof control is now established in the following form:

1. Rule: If θ is zero and w is zero, then v is equal to zero.

2. Rule: If θ is zero and w is small-positive, then v is equal tosmall-positive.

3. Rule: If θ is small-positive and w is zero, then v is equal tosmall-positive.

4. Rule: If θ is zero and w is small-negative, then v is equal tosmall-negative

and so on. The whole system can be described by such a field of coarse,approximate rules (usually values based on experience)."

OBJECT OF THE INVENTION

The object of the invention is now, to develop a control method and acontrol circuit which effects control using fuzzy logic such that themost important requirements of a control circuit--precision, stabilityand speed--are fulfilled with the least possible expense.

SUMMARY OF THE INVENTION

In a method in accordance with the first part of claim 1, this object isachieved in that, a plurality of control paths are served by only asingle fuzzy controller which is connected to the control paths on atime division multiplex basis.

In a control circuit in accordance with claim 2, this object is likewiseachieved in that, a plurality of control paths are served by only asingle fuzzy controller which is connected to the control paths on atime division multiplex basis.

BRIEF DESCRIPTION OF THE DRAWINGS

There is shown in

FIG. 1 a first embodiment of the invention;

FIG. 2 a second embodiment of the invention;

FIG. 3 a third embodiment of the invention;

FIG. 4 a fourth embodiment of the invention for a tracking control loopand a focusing control loop.

DETAILED DESCRIPTION

The first embodiment of the invention depicted in FIG. 1 will now beinitially described and thereafter its manner of operation will beexplained.

The output of a multiplexer MUX1 is connected to the input E1 of a fuzzycontroller FR whose output is connected to the input of a demultiplexerDEMUX. Each output of the demultiplexer DEMUX is connected to the inputofa respective control path RS1 to RSn. The output of each control pathRS1 to RSn is connected to a respective input of the multiplexer MUX1.

During the control operation, the adjustment signals for the individualcontrol paths RS1 to RSn at the output of the fuzzy controller FR aredistributed to the appertaining control paths by means of thedemultiplexer DEMUX. The control-difference at the output of eachcontrol path RS1 to RSn is passed on by means of the multiplexer MUX1 tothe inputE1 of the multiplexer MUX1.

The second embodiment of the invention depicted in FIG. 2 will now beinitially described and thereafter its manner of operation will beexplained.

The output of a multiplexer MUX1 is connected to the input E1 of a fuzzycontroller FR whose output is connected to the input of a demultiplexerDEMUX. Each output of the demultiplexer DEMUX is connected to the inputofa respective digital-analogue converter DA1 to DAn. The output of eachdigital-analogue converter DA1 to DAn is connected to the input of arespective control path RS1 to RSn. The output of each control path RS1toRSn is connected to the input of a respective analogue-digitalconverter AD11 to AD1n. The outputs of the analogue-digital convertersAD11 to AD1n are connected to the inputs of the multiplexer MUX1 . Theoutputs of a clock pulse generator TG are connected to the clock inputsof the demultiplexer DEMUX, the multiplexer MUX1 , the digital-analogueconverters DA1 to DAn and the analogue-digital converters AD11 to AD1n.

During the control operation, the analogue-digital converters AD11 toAD1n,the digital-analogue converters DA1 to DAn and also thedemultiplexer DEMUXand the multiplexer MUX1 are synchronised by theclock rate of the clock pulse generator TG so that the adjustmentsignals for the individual control paths RS1 to RSn at the output of thefuzzy controller FR are passed on to the appertaining control paths.

The intrinsic advantage of the invention resides here in that aplurality of control circuits are served by only a single fuzzycontroller which is connected to the individual control paths in timedivision multiplex. In accordance with the conventional method ofautomatic control, one controller would be required for each controlpath, which, moreover, wouldhave to be optimised in each control path.

In accordance with the invention, the fuzzy controller FR receives thecontrol-difference from each control path RS1 to RSn, which is deliveredby the multiplexer MUX1 in time division multiplex. The digital controlvalue required for each control-difference is produced in the fuzzycontroller FR from the table of values in accordance with the functionalrelationship and is emitted via the output of the fuzzy controller FR tothe input of the demultiplexer DEMUX which then passes the digitalcontrolvalues to the individual digital-analogue converters DA1 to DAn.Analogue adjustment signals now reach the individual control paths RS1to RSn from the digital-analogue converters DA1 to DAn.

A third embodiment is shown in FIG. 3 which is supplemented vis a visthe second embodiment of FIG. 2 by a second multiplexer MUX2, furtheranalogue-digital converters AD21 to AD2n and differentiating elements D1to Dn.

The output of each control path RS1 to RS2 is connected to the input ofa respective differentiating element D1 to Dn. The output of eachdifferentiating element D1 to Dn is connected to the input of arespectiveanalogue-digital converter AD21 to AD2n. The outputs of theanalogue-digital converters AD21 to AD2n are connected to the inputs ofthe multiplexer MUX2 whose output is connected to the second input E2 ofthe fuzzy controller FR. The clock pulse generator TG is connected tothe clock inputs of the analogue-digital converters AD21 to AD2n.

The adjustment signal is determined from the table of values in thefuzzy controller FR, by means of the functional relationship, from thecontrol-difference which is derivable at the output of the multiplexerMUX1, and, the differentiated control-difference which is derivable attheoutput of the multiplexer MUX2.

If the individual control paths RS1 to RSn are not too different, thenthe digital-analogue converters DA1 to DAn between the outputs of thedemultiplexer DEMUX and the control paths RS1 to RSn may be replaced byone digital-analogue converter between the output of the fuzzycontroller FR and the input of the demultiplexer DEMUX. Likewise, theanalogue-digital converters AD11 to AD1n as well as AD21 to AD2n may bereplaced by a respective analogue-digital converter between the cutputof the multiplexer MUX1 and the fuzzy controller FR and between themultiplexer MUX2 and the fuzzy controller FR.

A fourth embodiment is illustrated in FIG. 4. This is concerned with thefocusing control loop and the tracking control loop of an opticalreproduction device or of a magneto-optic recording and reproductiondevice.

In an optical reproduction device, in a CD player for example, a lightbeamis focused on the recording medium, the so-called compact disc, by afocusing control loop and is guided along the spiral-like data tracks ofthe compact disc by a tracking control loop.

The construction of the focusing control loop and tracking control loopshown in FIG. 3 will now be described.

The output of a fuzzy controller FR is connected to the input of ademultiplexer DEMUX whose first output is connected to the input of adigital-analogue converter DA1 and whose second output is connected totheinput of a digital-analogue converter DA2. The output of thedigital-analogue converter DA1 is connected via an amplifier V1 to theinput of the control path RS1 whose output is connected to the input ofanamplifier V2. The output of the digital-analogue converter DA2 isconnectedto the input of an amplifier V3 whose output is connected tothe input of the control path RS2. The output of the control path RS2 isconnected to the input of an amplifier V4 whose output is connected tothe input of an analogue-digital converter AD12. The output of theamplifier V2 is connected to the input of an analogue-digital converterAD11. The outputs of the two analogue-digital converters AD11 and AD12are connected to the inputs of a multiplexer MUX1 whose output isconnected to the first input of the fuzzy controller FR. The output ofthe control path RS2 is moreoverconnected to the input of a firstdifferentiating element D1 whose output is connected to the input of anamplifier V5. The output of the control path RS2 is connected to theinput of a differentiating element D2 whose output is connected to theinput of an amplifier V6. The output of the amplifier V5 is connected tothe input of an analogue-digital converter AD21 whose output isconnected to the first input of a multiplexer MUX2. The output of theamplifier V6 is connected to the input of an analogue-digital converterAD22 whose output is connected to the second input of the multiplexerMUX2. The output of the multiplexer MUX2 is connected to the secondinput E2 of the fuzzy controller. A clock pulse generator TG deliversthe clock pulses for the demultiplexer DEMUX, the multiplexers MUX1 andMUX2, the digital-analogue converters DA11, DA12, the analogue-digitalconverters AD11, AD12, AD21 and AD22.

The control path RS1 is the focusing control path while the control pathRS2 represents the tracking control path. The amplifiers V1 to V6 servefor level matching. For each focusing error signal FE which the focusingcontrol path RS1 emits, the fuzzy controller searches in the table ofvalues for the appertaining adjustment value with the aid of thedifferentiated focusing error signal. The fuzzy controller FR likewisesearches in the table of values for the adjustment value appertaining toeach tracking error signal TE at the output of the tracking control pathRS2 with the aid of the differentiated tracking error signal. Thefocusingcontrol path and the tracking control path thus alternatelyreceive an adjustment signal on a time division multiplex basis.

The invention is not in any way limited to the servo-loops--the focusingcontrol loop and the tracking control loop--of a CD player however, butisapplicable over the whole field of automatic control systems. Forexample, the invention can, in advantageous manner, be utilised in knownanti-blocking braking systems in vehicles, and generally in chemicalprocess control, for example, exhaust gas purification plants.

In summary, the substantial advantages of the invention will beenumerated once more: a saving of controllers, a simple and universalapplicability in the field of automatic control since optimisation isonly required once, no adjustment of the servo-amplification, a virtualindependence of alterations of the components and no drift of thecontrol parameters as the result of temperature fluctuations.

I claim:
 1. A control circuit which effects control using fuzzy logic,comprising:a plurality of control paths (RS1, RS2, . . . , RSn); asingle fuzzy controller (FR); a first multiplexer (MUX1) having aplurality of inputs and having an output coupled to a first input (E1)of the fuzzy controller (FR); a demultiplexer (DEMUX) having an inputcoupled to an output of said fuzzy controller and having a plurality ofoutputs; a plurality of digital-analogue converters respectively coupledbetween respective outputs of said first demultiplexer and respectiveinput connections of respective ones of said control paths; a firstplurality of analogue-digital converters (AD1, AD2, . . . , ADn)respectively coupled between respective inputs of said first multiplexerand respective output connections of respective ones of said controlpaths; a plurality differentiating elements (D1, D2, . . . , Dn), havingrespective input connections coupled to output connections of respectiveones of said control paths and having respective outputs; a secondplurality of analogue-digital converters (AD21, AD22, . . . , ADn)having respective inputs coupled to respective outputs of saiddifferentiating elements; and having respective outputs; a seconddemultiplexer (DEMUX 2) having an output connected to a second input(E2) of the fuzzy controller (FR) and having a plurality of inputconnections respectively coupled to respective outputs of said secondplurality of analogue-digital converters; and wherein said first andsecond multiplexers and said demultiplexer are conditioned to couplesaid fuzzy controller in a closed loop, sequentially with a control pathand exclusive of other control paths.
 2. Control circuit in accordancewith claim 1, characterised in that, the digital control values for theindividual control paths (RS1, RS2, . . . , RSn) are stored in a tableof values in the fuzzy controller (FR).
 3. A control circuit whicheffects control using fuzzy logic, comprising:a single fuzzy controller(FR) for the focusing control loop and the tracking control loop of anoptical reproduction device or a magneto-optic recording andreproduction device in order to focus the light beam which is scanningthe data on a disc-like recording medium onto the recording medium andto guide it along the data tracks of the recording medium; a pluralityof control paths (RS1, RS2, . . . , RSn) including a focusing controlpath and a tracking control path; a time division multiplexer forsequentially and exclusively connecting respective ones of the controlpaths (RS1, RS2, . . . , RSn) concurrently to an input and an output ofthe fuzzy controller on a time division multiplex basis and wherein saidfuzzy controller provides a control signal to a respective control pathduring respective connections of the sequence.
 4. Control circuit inaccordance with claim 3, characterized in that, the output of a firstmultiplexer (MUX1) is connected to the first input (E1) of the fuzzycontroller (FR) whose output is connected to the input of ademultiplexer (DEMUX), that each output of the demultiplexer (DEMUX) isconnected to the input to a respective control path (RS1, RS2, . . . ,RSn) and that the output of each control path (RS1, RS2, . . . , RSn) isconnected to a respective input of the first multiplexer (MUX1). 5.Control circuit in accordance with claim 3, characterized in that, theoutput of a first multiplexer (MUX1) is connected to the first input(E1) of the fuzzy controller (FR) whose output is connected to the inputof a demultiplexer (DEMUX), that each output of the demultiplexer(DEMUX) is connected to the input of a respective digital-analogconverter (DA1, DA2, . . . , DAn), that a control path (RS1, RS2, . . ., RSn) follows each digital-analog converter (DA1, DA2, . . . , DAn),that an analog-digital converter (AD11, AD12, . . . , AD1n) follows eachcontrol path (RS1, RS2, . . . , RSn) and that the outputs of theanalog-digital converters (AD11, AD12, . . . , AD1n) are connected tothe inputs of the first multiplexer (MUX1).
 6. Control circuit inaccordance with claim 3, characterized in that, the digital controlvalues for the individual control paths (RS1, RS2, . . . , RSn) arestored in a table of values in the fuzzy controller (FR).
 7. A controlcircuit which effects control using fuzzy logic, comprising:a singlefuzzy controller (FR) for a focusing control loop and a tracking controlloop of an optical reproduction device or a magneto-optic recording andreproduction device for focusing a scanning light beam on a disc-likerecording medium and to guide it along data tracks of the recordingmedium; a plurality of control paths (RS1, RS2, . . . , RSn) includingsaid focusing control loop and said tracking control loop; a firstmultiplexer (MUX1 having a plurality of inputs and having an outputcoupled to a first input (E1) of the fuzzy controller (FR); ademultiplexer (DEMUX) having an input coupled to an output of said fuzzycontroller, and having a plurality of outputs; a plurality ofdigital-analogue converters respectively coupled between respectiveoutput of said first demultiplexer and respective input connections ofat least said focusing control loop and said tracking control loop; afirst plurality of analogue-digital converters (AD1, AD2, . . . , ADn)respectively coupled between respective inputs of said first multiplexerand respective output connections of respective ones of said controlpaths including said focusing control loop and said tracking controlloop; a plurality differentiating elements (D1, D2, . . . , Dn), havingrespective input connections coupled to output connections of respectiveones of said control paths and having respective outputs; a secondplurality of analogue-digital converters (AD21, AD22, . . . , ADn)having respective inputs coupled to respective outputs of saiddifferentiating elements; and having respective outputs; a seconddemultiplexer (DEMUX 2) having an output connected to a second input(E2) of the fuzzy controller (FR) and having a plurality of inputconnections respectively coupled to respective outputs of said secondplurality of analogue-digital converters; and wherein said first andsecond multiplexers and said demultiplexer are conditioned to couplesaid fuzzy controller in a closed loop, sequentially with a control pathand exclusive of other control paths.